1. Field of the Invention
This invention relates to a free cutting stainless steel, and more particularly to an austenitic free cutting stainless steel containing Bi as a necessary free cutting element for the provision of free cutting properties.
2. Related Art Statement
In general, stainless steels are large in the viscosity, poor in the heat conductivity, and are apt to be coherent to a tool in the cutting, so that they are difficult to be subjected to the cutting work. Therefore, it has been studied and developed to improve the free cutting properties of the stainless steel by the addition of a free cutting element such as S, Pb, Bi, Te, Se or the like, and the resulting steels have been applied to various uses as a free cutting stainless steel.
In the free cutting stainless steel of this type, however, the free cutting properties are improved by the addition of the free cutting element, but the hot workability is inversely degraded due to the addition of such a free cutting element, which comes into problem in the production. In the austenitic stainless steel, the hot workability is not so good, and is considerably degraded by adding the free cutting element.
Furthermore, the stainless steel is utilized in wide applications owing to the corrosion resistance. Particularly, the austenitic stainless steel has an excellent corrosion resistance, so that it is suitable for various application. However, the application of such steels may be restricted due to the presence of the free cutting element. For example, the addition of S, Pb, Te, Se and the like comes into problem in the corrosion resistance and food hygiene when the steel is used as a material for food machines, and particularly the addition of Pb can not be adopted due to the latter problem. On the other hand, since Bi is an element used in chemicals, cosmetics and the like, it has been considered that Bi is optimum to be applied to free cutting stainless steels for use in the food machine, but the addition of Bi considerably degrades the hot workability, which comes into problem in view of the production.